1. Field of the Invention
The invention pertains to the treatment of liquids. More specifically, the invention relates to a method and a device for treating a liquid, in particular for separating different constituents contained in the liquid, for removing pollutants from the liquid or for sterilizing the liquid. The liquid is thereby introduced into a vacuum tank in which a part thereof is evaporated, and the remaining part thereof is discharged from the vacuum tank, the liquid in the vacuum tank flowing under the effect of gravity to a fixed surface on which a liquid film develops from which the vaporous phase emerges.
It has been known heretofore from Austrian patent AT-PS 377 244 to remove pollutants from a liquid by spraying the liquid in to a vacuum tank. As a result, those constituents contained in the liquid, which have a lower boiling point than the liquid itself, are evaporated, thus bringing about the desired separation. Using this method, furthermore, owing to the fact that azeotropic mixtures develop, pollutants whose boiling point is higher than that of the liquid can be extracted from the liquid with the vaporous phase.
However, this previously known method does not, in many respects, meet all the requirements:
In order to achieve the desired small droplet size, the liquid must be passed through a spraying nozzle at a high pressure, and a pump must be provided for this purpose. This causes additional outlay in setting up a plant to carry out the method. Additionally, further operating costs are incurred by the pump.
Furthermore, due to the fact that the liquid is sprayed upwards, the droplets being ejected collide with the descending droplets. As a result, they combine to form larger droplets and the degree of efficiency of the process is diminished.
Furthermore, since the droplets sprayed out are only subjected to the vacuum for a short time and then collect at the bottom of the tank, the vacuum prevailing in the tank acts only on that part of the liquid which is located at the surface of the liquid collected in the tank, as a result of which only a low degree of efficiency can likewise be achieved.
Furthermore, devices are known from German patent publication DE-A 29 27 661, from international publication WO 94/25132, and from European patent publication EP-A 166 790, with vacuumized tank into which liquids to be treated are introduced and then vaporized in the tank. For this purpose, the liquids flow along vertical surfaces within the tank, during which process they are subjected to the vacuum.
Those prior art devices, however, have in common a very poor degree of efficiency. This is mostly due to the fact that the liquid flowing along the surfaces has a very short residence time and the liquid is exposed only briefly to the vacuum because the surfaces are disposed vertically.